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A large clinical trial referred to as the Sister Study, which is currently enrolling patients, will address the issues of environmental factors and genetics in the development of breast cancer.

Breast cancer is diagnosed in one out of every eight women in the United States. A diagnosis of cancer not only affects the patient, but also deeply affects a patient’s children, spouse, parents, brothers, sisters, and friends.

Although long-term outcomes and cure rates for breast cancer have come a long way in the past decades, the ultimate goal of research would be to prevent the disease altogether, beginning with an understanding of variables that may increase the risk of breast cancer.

A hotly debated issue surrounding breast cancer concerns environmental factors that may be playing a role in the development of the disease. There are some factors known to contribute to the risk of developing breast cancer; they include diet, exercise, hormone therapy, breast-feeding, and smoking. However, the prevalence of the disease (over 200,000 women are diagnosed every year), suggests that there may be other factors at play.

The Sister Study is planning to accrue 50,000 women aged 35–74 years who have at least one sister related by blood diagnosed with breast cancer. Currently, 35,000 women have already been enrolled into the trial. The Sister Study is being conducted by the National Institute of Environmental Health Sciences and will be evaluating women from all backgrounds, occupations, races, and ethnicities to attempt to identify environment and genetic factors that may be associated with affecting the risk of breast cancer.

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Women who fit the following criteria are urged to enroll in the Sister Study to join the fight against this disease:

  • Have a sister related by blood, alive or deceased, diagnosed with breast cancer
  • Are between the ages of 35–74 years
  • Live in the United States or Puerto Rico

“Many women have heard about the Sister Study, but they haven’t signed up yet, and we really need them now,” said Dale Sandler, Ph.D., Chief of the Epidemiology Branch at NIEHS and Principal Investigator of the Sister Study. “Doctors know very little about how the environment may affect breast cancer, that is why the Sister Study is so important. We hope women will make that call today,” she added.

The Sister Study is available in English and Spanish and can be done from home when it is convenient for women. To learn more about the Sister Study, visit the web site, or for Spanish visit A toll-free number is also available 1-877-4SISTER (877-474-7837). Deaf/Hard of Hearing call 1-866-TTY-4SIS (866-889-4747).

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